The advantages of operating an auxiliary engine during periods of shutdown of the primary diesel truck engine are well known. Most auxiliary engine systems have been built for the purpose of operating the truck's electrical systems without the need for operation of the primary engine. Some auxiliary engine systems provide for the operation of climate control devices. As a result, such auxiliary engine systems have made it possible to heat or cool the cab of the truck as well as to provide electrical power at significantly less expense than would be associated with the idling of the primary engine. In addition, such systems reduce wear to the primary diesel engine caused by extended periods of idling and by cold starting.
Two examples of existing auxiliary engine systems are disclosed in U.S. Pat. No. 4,825,663 to Nijjar et al., "Auxiliary Air Conditioning System for Trucks and Other Heavy Duty Vehicles," and in U.S. Pat. No. 4,531,379 to Diefenthaler, Jr., "Auxiliary Power System for Vehicle Air Conditioner and Heater." Nijjar et al. show the use of a secondary engine which generates electrical power during periods of shutdown of the primary engine. The secondary engine is also used to drive an auxiliary air conditioning system associated with the Nijjar et al. auxiliary system. The coolant system of the secondary engine is connected to the coolant system of the primary engine in order to allow the primary engine to be warmed by waste heat from the secondary engine. Auxiliary systems such as that disclosed by Nijjar et al. add weight and expense to the operation and maintenance of the truck, particularly to the extent that they utilize redundant compressors, condensers, and pumps.
The auxiliary power system disclosed by Diefenthaler, Jr. utilizes a secondary motor to drive the compressor of the truck's air conditioning system thereby eliminating the need for an auxiliary compressor. Heat from the secondary engine is selectively delivered to either the interior of the truck or to a water tank. However, the Diefenthaler, Jr. system also employs some duplicative components, such as a redundant water pump and a redundant alternator.